长链非编码RNA——抗病毒天然免疫应答的新兴调控因子

长链非编码RNA(long non-coding RNAs, lncRNAs)是长度超过200nt的非编码RNA分子的总称。作为一类重要的基因调控因子,lncRNAs在表观遗传学、转录及转录后等多个水平调控靶基因的表达。近年来的研究表明,许多lncRNAs可被病毒或干扰素(interferon, IFN)诱导表达,并作为调控因子在IFN介导的抗病毒天然免疫应答中调节抗病毒相关基因的表达。本文重点阐述了lncRNAs在IFN介导的抗病毒天然免疫应答中的调控作用,尤其是对干扰素刺激基因(interferon-stimulated genes, ISGs)转录的调控作用,并归纳了lncRNAs、IFN和ISGs形成的调控网络,以期为从事lncRNAs调控IFN介导的抗病毒天然免疫应答机制研究的相关科研人员提供参考。     

ICP0 prevents RNase L-independent rRNA cleavage in herpes simplex virus type 1-infected cells

The classical interferon (IFN)-dependent antiviral response to viral infection involves the regulation of IFN-stimulated genes (ISGs), one being the gene encoding cellular endoribonuclease RNase L, which arrests protein synthesis and induces apoptosis by nonspecifically cleaving rRNA. Recently, the herpes simplex virus type 1 (HSV-1) protein ICP0 has been shown to block the induction of ISGs by subverting the IFN pathway upstream of the 2'-5'-oligoadenylate synthetase (OAS)/RNase L pathway. We report that ICP0 also prevents rRNA degradation at late stages of HSV-1 infection, independent of its E3 ubiquitin ligase activity, and that the resultant rRNA degradation is independent of the classical RNase L antiviral pathway. Moreover, the degradation is independent of the viral RNase vhs and is independent of IFN response factor 3. These studies indicate the existence of another, previously unidentified, RNase that is part of the host antiviral response to viral infection.     

TRIM56 Is an Essential Component of the TLR3 Antiviral Signaling Pathway

Members of the tripartite motif (TRIM) proteins are being recognized as important regulators of host innate immunity. However, specific TRIMs that contribute to TLR3-mediated antiviral defense have not been identified. We show here that TRIM56 is a positive regulator of TLR3 signaling. Overexpression of TRIM56 substantially potentiated extracellular dsRNA-induced expression of interferon (IFN)-β and interferon-stimulated genes (ISGs), while knockdown of TRIM56 greatly impaired activation of IRF3, induction of IFN-β and ISGs, and establishment of an antiviral state by TLR3 ligand and severely compromised TLR3-mediated chemokine induction following infection by hepatitis C virus. The ability to promote TLR3 signaling was independent of the E3 ubiquitin ligase activity of TRIM56. Rather, it correlated with a physical interaction between TRIM56 and TRIF. Deletion of the C-terminal portion of TRIM56 abrogated the TRIM56-TRIF interaction as well as the augmentation of TLR3-mediated IFN response. Together, our data demonstrate TRIM56 is an essential component of the TLR3 antiviral signaling pathway and reveal a novel role for TRIM56 in innate antiviral immunity.     

Subcellular localization and functional characterization of a fish IRF9 from crucian carp Carassius auratus

Mammalian interferon (IFN) regulatory factor 9 (IRF-9) has long been recognized as the DNA sequence recognition subunit of IFN-stimulated gene factor 3 (ISGF3) complex, which is critical for type I IFN to induce the expression of IFN-stimulated genes (ISGs) against viral infection. Recent studies have shown that fish IFN exerts antiviral effects by induction of a number of ISGs and also of itself; however, little is known about the role of fish IRF9 in IFN signaling. Here we identify a fish IRF9 orthologue (CaIRF9) from IFN-producing cell line, crucian carp Carassius auratus blastulae embryonic (CAB) cells. Analysis of subcellular distribution of CaIRF9-green fluorescent protein indicates that CaIRF9 is constitutively present in the nucleus, which is driven by two nuclear localization signals (NLS), one locating within DNA-binding domain (DBD) of CaIRF9 and the other immediately behind DBD, although human IRF9 contains only one NLS analogous to the former of CaIRF9. Overexpression of CaIRF9 together with CaSTAT2 not only activates ISRE-containing promoter but also upregulates the expression of fish ISGs. Strikingly, CaIRF9 together with CaSTAT2 also exhibits an ability to activate crucian carp IFN promoter, and blockade of cellular CaIRF9 attenuates IFN itself-induced activation of crucian carp IFN promoter. Taken together, these data suggest that crucian carp IFN induces the expression of ISGs and also of itself possibly by the JAK-STAT signaling pathway that is conserved from fish to mammals.     

The Differential Antiviral Activities of Chicken Interferon α (ChIFN-α) and ChIFN-β are Related to Distinct Interferon-Stimulated Gene Expression

Chicken interferon α (ChIFN-α) and ChIFN-β are type I IFNs that are important antiviral cytokines in the innate immune system. In the present study, we identified the virus-induced expression of ChIFN-α and ChIFN-β in chicken fibroblast DF-1 cells and systematically evaluated the antiviral activities of recombinant ChIFN-α and ChIFN-β by cytopathic-effect (CPE) inhibition assays. We found that ChIFN-α exhibited stronger antiviral activity than ChIFN-β in terms of inhibiting the replication of vesicular stomatitis virus, Newcastle disease virus and avian influenza virus, respectively. To elucidate the mechanism of differential antiviral activities between the two ChIFNs, we measured the relative mRNA levels of IFN-stimulated genes (ISGs) in IFN-treated DF-1 cells by real-time PCR. ChIFN-α displayed greater induction potency than ChIFN-β on several ISGs encoding antiviral proteins and MHC-I, whereas ChIFN-α was less potent than ChIFN-β for inducing ISGs involved in signaling pathways. In conclusion, ChIFN-α and ChIFN-β presented differential induction potency on various sets of ISGs, and the stronger antiviral activity of ChIFN-α is likely attributed to the greater expression levels of downstream antiviral ISGs.     

Efficacy of IFN-λ1 to Protect Human Airway Epithelial Cells against Human Rhinovirus 1B Infection

Impaired interferon (IFN) production has been observed in various obstructive respiratory diseases. This contributes to enhanced sensitivity towards viral infections triggering acute exacerbations. To compensate for this impaired host IFN response, there is need to explore new therapeutic strategies, like exogenous administration of IFNs as prophylactic treatment. In the present study, we examined the protective potential of IFN-λ1 and compared it with the previously established protecting effect of IFN-β. A549 cells and human primary bronchial epithelial cells were first treated with either IFN-β (500 IU/ml) or IFN-λ1 (500 ng/ml) for 18 h. For infection, two approaches were adopted: i) Continuous scenario: after pre-treatment, cells were infected immediately for 24 h with human rhinovirus 1B (HRV1B) in IFN-containing medium, or were cultured for another 72 h in IFN-containing medium, and then infected for 24 h with HRV1B, ii) Pre-treatment scenario: IFN-containing medium was replaced after 18 h and cells were infected for 4 h either immediately after pre-treatment or after additional culturing for 72 h in IFN-free medium. The protective effect was evaluated in terms of reduction in the number of viral copies/infectious progeny, and enhanced expression of IFN-stimulated genes (ISGs). In both cell types and in both approaches, IFN-λ1 and IFN-β treatment resulted in pronounced and long-lasting antiviral effects exemplified by significantly reduced viral copy numbers and diminished infectious progeny. This was associated with strong up-regulation of multiple ISGs. However, in contrast to the IFN-β induced expression of ISGs, which decreased over time, expression of ISGs induced by IFN-λ1 was sustained or even increased over time. Here we demonstrate that the protective potential of IFN-λ1 is comparable to IFN-β. Yet, the long-lasting induction of ISGs by IFN-λ1 and most likely less incitement of side effects due to more localized expression of its receptors could make it an even more promising candidate for prophylactic treatment than IFN-β.     

Antiviral Responses by Swine Primary Bronchoepithelial Cells Are Limited Compared to Human Bronchoepithelial Cells Following Influenza Virus Infection

Swine generate reassortant influenza viruses because they can be simultaneously infected with avian and human influenza; however, the features that restrict influenza reassortment in swine and human hosts are not fully understood. Type I and III interferons (IFNs) act as the first line of defense against influenza virus infection of respiratory epithelium. To determine if human and swine have different capacities to mount an antiviral response the expression of IFN and IFN-stimulated genes (ISG) in normal human bronchial epithelial (NHBE) cells and normal swine bronchial epithelial (NSBE) cells was evaluated following infection with human (H3N2), swine (H1N1), and avian (H5N3, H5N2, H5N1) influenza A viruses. Expression of IFNλ and ISGs were substantially higher in NHBE cells compared to NSBE cells following H5 avian influenza virus infection compared to human or swine influenza virus infection. This effect was associated with reduced H5 avian influenza virus replication in human cells at late times post infection. Further, RIG-I expression was lower in NSBE cells compared to NHBE cells suggesting reduced virus sensing. Together, these studies identify key differences in the antiviral response between human and swine respiratory epithelium alluding to differences that may govern influenza reassortment.     

Basal expression levels of IFNAR and Jak-STAT components are determinants of cell-type-specific differences in cardiac antiviral responses

Viral myocarditis is an important human disease, and reovirus-induced murine myocarditis provides an excellent model system for study. Cardiac myocytes, like neurons in the central nervous system, are not replenished, yet there is no cardiac protective equivalent to the blood-brain barrier. Thus, cardiac myocytes may have evolved a unique antiviral response relative to readily replenished cell types, such as cardiac fibroblasts. Our previous comparisons of these two cell types revealed a conundrum: reovirus T3D induces more beta-interferon (IFN-β) mRNA in cardiac myocytes, yet there is a greater induction of IFN-stimulated genes (ISGs) in cardiac fibroblasts. Here, we investigated possible underlying molecular determinants. We found that greater basal expression of IFN-β in cardiac myocytes results in greater basal activated nuclear STAT1 and STAT2 and greater basal ISG mRNA expression and provides greater basal antiviral protection relative to cardiac fibroblasts. Conversely, cardiac fibroblasts express greater basal IFN-α/β receptor 1 (IFNAR1) and greater basal cytoplasmic Jak1, Tyk2, STAT2, and IRF9, leading to a greater increase in reovirus T3D- or IFN-induced nuclear activated STAT1 and STAT2 and greater induction of ISGs for a greater IFN-induced antiviral protection relative to cardiac myocytes. Our results suggest that high basal IFN-β expression in cardiac myocytes prearms this vulnerable, nonreplenishable cell type, while high basal expression of IFNAR1 and latent Jak-STAT components in adjacent cardiac fibroblasts renders these cells more responsive to IFN and prevents them from inadvertently serving as a reservoir for viral replication and spread to cardiac myocytes. These studies provide the first indication of an integrated network of cell-type-specific innate immune components for organ protection.     

RNA-activated protein kinase differentially modulates innate immune response mediated by supraphysiological concentrations of thyroid hormone

Nuclear hormone receptor ligands are known to modulate innate immunity by dampening the immune response induced by pathogens. Here, we report that unlike other ligands, 3,3′,5-triiodo-l-thyronine (T3) induced the type 1 IFN response and expression of IFN-stimulated genes (ISGs). T3 action was found to be significantly amplified at supraphysiological concentrations (SPC) and in combination with double-stranded RNA mimic polyinosinic–polycytidylic acid. Induction by T3 was due to non-genomic mechanisms involving integrin binding, calcium mobilization, and phosphatidyl-inositol 3-kinase–AKT pathways, but was independent of TLR3, RIG-I, and IFN-β1 pathways. Whereas siRNA-induced knockdown of RNA-activated protein kinase (PKR) was found to abrogate the T3-induced expression of select ISGs, expression of other T3-induced ISGs was strongly induced by PKR knockdown, indicating the differential role of PKR in modulating T3 action. Together, we describe a novel role of T3 in modulating the innate immune response and identify the importance of PKR in regulating T3-induced immune activation. These findings have important implications in the basic understanding of the mechanisms of T3 function at SPCs and crosstalk involved in the thyroid hormone function and the innate immune response.     

Expression of interferon and interferon-induced genes in salmonids in response to virus infection, interferon-inducing compounds and vaccination

Interferons (IFNs) involved in innate immunity against viruses have recently been cloned from Atlantic salmon and rainbow trout. Moreover, several IFN-stimulated genes (ISGs) have been cloned from salmonids although only Mx has been shown to possess antiviral properties. Much less in known about how viruses induce IFNs in salmonids, but synthetic ligands for some of the main mammalian viral sensors also induce IFNs and ISGs in salmonids. Analysis of the promoters of the salmon IFN-alpha1 and IFN-alpha2 genes shows that activation is dependent on both NFkappaB and IRFs similar to human IFN-beta. Furthermore, several IFN-stimulated genes (ISGs) have been cloned from salmonids although only Mx has been shown to possess antiviral properties. The synthetic compounds poly I:C, imidazoquinolines and CpG oligonucleotides induce IFNs and ISGs in salmonids, probably through the same pathways as in mammals. Salmonid viruses show potent ability to stimulate expression of IFN and ISGs in vivo. Differences between viruses in the ability to stimulate host gene expression are often more evident in cell culture, but more work is needed to pinpoint how salmonid viruses antagonize the IFN system of their host. Finally, existing data suggest that IFNs play a role in the early non-specific protection observed after vaccination of salmonids with rhabdoviral DNA vaccines and conventional polyvalent vaccines.